The present invention relates generally to radars, and more particularly, to a motion detection radar system that is adapted to produce radar warnings signals regarding the presence of moving objects that are located behind structural barriers, and the like.
Law enforcement agencies have an urgent need for a low cost, easily portable, system for detecting the presence of people inside buildings or behind walls where the subjects cannot be seen. The system must have the capability to penetrate most common building materials such as wood, stucco and concrete. It is also necessary for the system to penetrate bushes, shrubs, and other foliage. It must provide a positive indication of people moving at distances of at least 20 feet on the other side of the barrier. It must be able to look through both common floors and ceilings. The system must be battery operated and provide for remote, wire free operation.
A number of different types of radars have been developed that can detect the motion of a person in a clear environment. Most of these radars are doppler radars. A doppler radar measures the motion of a object in terms of the difference in frequency of the received radar signal as compared to the frequency of the transmitted radar signal. The motion of the object causes this change in frequency in the same way that the sound of the whistle of a passing train changes. The doppler frequency difference is equal to two times the speed of the object (toward or away from the radar) times the operating frequency of the radar divided by the speed of transmission (983,57 1,000 feet per second). Thus, as the radar frequency is increased, so does the doppler frequency for the same speed object.
A radar operating at 983.571 MHz, for example, would produce a 2 Hz doppler frequency for a object motion of 1 foot per second, (2.times.1 ft/sec .times.1 Hz/f/sec =2 Hz). Consequently, for motion less than 1 ft/sec, it is necessary to measure phase difference rather than frequency difference because the doppler frequency is so low. Therefore, for slow moving object situations, doppler radar is not the optimally adapted for use in this application.
Accordingly, it is an objective of the present invention to provide for a motion detection radar system that is adapted to produce radar warnings signals regarding the presence of moving objects that are located behind structural barriers, and the like.